It seems I have a "rogue" interior elevation view. I cannot find its plan view symbol anywhere. I created a new plan view for that floor which had all elevation symbols turned on, and it's not there.
Normally if you click the crop region in an elevation view, then Ctrl-Tab back to the plan view, the elevations cut line and view depth will be visible in the plan. But for this particular elevation view, no such lines or other notation is visible.
There are no scope boxes involved. How could this have happened?